1. Field of the Invention
The present invention relates to a linear solenoid valve for generating an electromagnetic force in proportion to an amount of current supplied to a solenoid and displacing a valve element under the generated electromagnetic force.
2. Description of the Related Art
There have been used in the art electromagnetic valves for displacing a valve element by attracting a movable core to a fixed core under an electromagnetic force that is generated when a solenoid coil is energized.
Japanese Utility Model Laid-Open Publication No. 63-56371, for example, discloses a technical idea for coating the entire surface of a movable core of a solenoid-operated valve with a nonmagnetic, wear-resistant thin film for suppressing a reduction in the density of magnetic fluxes produced by a magnetic circuit of the solenoid-operated valve.
With the solenoid-operated valve disclosed in Japanese Utility Model Laid-Open Publication No. 63-56371, however, since the entire surface of the movable core, which is of a predetermined diameter, is coated with the thin film, the outside diameter of the movable core is increased by the thickness of the thin film. Consequently, it is necessary to manage not only the outside diameter of the movable core itself, but also the thickness of the applied thin film.
Furthermore, because the thin film applied to the entire surface of the movable core may possibly be peeled off or swollen on the outer surface of the movable core, the disclosed solenoid-operated valve needs to incorporate some countermeasures for preventing the thin film from being peeled off or swollen on the outer surface of the movable core.
There is a demand for increased coaxial alignment between a yoke and a fixed core of the solenoid-operated valve for reducing hysteresis that occurs when the movable core is reciprocally moved.